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I Just Bought 30 435w Commercial Solar Panels...Now What

Ralo

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This is for a totally offgrid system.

I have two of the H model DC Solar trailers which have two SMA 6048 inverters each and one Midnite Solar 250 each. Each trailer also has 10 - 265w solar panels and 2 520ah forklift battery. I'm in Louisiana and get very few clear days so solar generation is poor. My idea to compensate for the lack of sunshine was to buy as many solar panels as I could, but I think I screwed up.

I bought what I thought was the best used panels available on ebay, 30 SunPower 435w commercial panels. They are hugh but I can get all 30 on the roof of my metal building, although half of them will point slightly north. I didn't think that was too big of a deal since most days are cloudly anyway. That's not my biggest concern.

What I need to know now is what charge controllers do I need to handle all these solar panels. Sunnyboy string inverters have been suggested on the Facebook forum, but I don't need additional inverters, I just need charge controllers. Now if the Sunnyboy can replace the Sunny Island inverters, then that may be a viable solution, however, I don't believe the Sunnyboy will charge my batteries or use battery power. I think they are solar only, but I could be wrong.

Anyway, is the best solution to just replace my current inverters and charge controllers with all-in-one units like the MPP LV6548? I would need two of them for 240v. Can two of these handle 13kw (on a good day) of solar? I thought I would be able to get away with just adding a few more Midnite 250's, but the open circuit voltage of these panels is 85.6v volts, so the strings would only consist of 3 panels. How many strings can I connect? Is that determined by the wattage of the panels?

As you can see, I am very confused and need some guidance. What is the simplest, most cost effective option?
 

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Could you please post a picture of the specs sticker on the panel, or a reference link showing all the panel specs? That link above doesn't seem to work for me.
 
Correct link to panel spec sheet (pdf):


85.6Voc, so you need to have either all panels in parallel, or have a charge controller that can handle (at least) around 230V (with a decent safety margin for cold weather) if you want to put two in series, which LV6548 will do. Two of them should be fine, since each can handle 8kW input I believe.

I thought I would be able to get away with just adding a few more Midnite 250's the open circuit voltage of these panels is 85.v volts, so the strings would only consist of 3 panels. How many strings can I connect? Is that determined by the wattage of the panels?

You'd be limited to two panels per string, since your Voc will rise as temperature drops - you need a safety margin. The Midnite also has a limit of 3kW solar input, so you'd need about four of them.
 
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I think the best thing to do is identify a power requirement, and then go to an off grid calculator like in my signature block and figure out how many kw of panels and kwh of battery storage ou need to make this work.


Also in my signature block is the basics if off grid design. This shows how to identical requirements like in Arizona where I live, and Seattle Washington, similar to where you live how the requirements are much larger for the poorer sun area.



For reference, most of my “lightly” overcast days where the sun is just barely obscured by a light overcast layer, I get 1/6th the rated power of my panels, but on a truly gray overcast day, I get 1/20th th rated output. If your trying to overpanel in those conditions, you also have to be careful not to exceed the max charge capacity of the batteries which limit you to lithium and you can’t use lead acid.

There is nothing wrong with a generator for cloudy days.
 
I think the best thing to do is identify a power requirement, and then go to an off grid calculator.
I'm trying to use the batteries and the panels I already have.
 
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Could you please post a picture of the specs sticker on the panel, or a reference link showing all the panel specs? That link above doesn't seem to work for me.
 

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I already have all the components. I want to know how to use what I have.

You had mentioned about possibly getting some LV6548s or something. A good thing about stacking multiple inverters is you get more PV Inputs that way. A pair of LV6548s have total of 4 PV Inputs.

With this many panels you need to determine what is the best wiring configuration (series/parallel) to use on the solar panels so any one string's Voc doesn't go over the max PV input voltage of the inverter.

Cold temp also drive up the actual Voc on the string's circuit, so use a calculator (unless you know the math), to figure out how many you can safely wire in series, and look at panel's Vmp and make sure it doesn't exceed the PV input's max amps or watts.


Your Voc on those panels is very high (85.6v), so you can't wire as many in series (that's only 2 panels in series on an inverter with 250v max PV input, could do more in parallel up to max Vmp).

The LV6548 has a max PV input of 250v, but it can take 8000w total (4000w x 2)...

As you said, the LV6548 requires the pair in order to operate in split-phase, and can stack up to 3x on L1 + 3x on L2 to get more amps in split-phase, and more PV inputs.
 
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I'm trying to use the batteries and the panels I already have.
By the way I do my calculations, I get 23 kwh possible per day useable With the batteries you have. The only problem I see is being able to make and not exceed the max charge rate, which my guess is 120 amps. At worst, what this may be is buying one or two more SCCs to feed your battery bank.

With that, and two 520 ah batteries, charging is limited to 120 amps max IF they can be charged at the 1/8th the 20 hour rate of the batteries. My Spec sheet for my FLA Trojans limit to that. To not go below 50% after two days, that is around 480ah usable per day or a daily power requirement of 23 kwh.

With 13 kw of panels, that would be enough, properly configured to run this on most days. This is what I came up with off the calculator:

866900DF-3990-4688-9AB4-E79F1555A675.pngSo, looks like you have plenty of panels to make those 23 kwh each day. This is supposed to include weather, which I think accounts for the drop in possible production in the summer, but this doesn’t take into account the # of days you won’t have sun for three or more days which means turning the generator on.

There could be more than 23 kwh produced per day if the batteries are done early enough. As long as you get those 120 amps charging, that’s close to 5 kw you can pull off the SCCs without dipping into the batteries.
 
With that, and two 520 ah batteries, charging is limited to 120 amps max IF they can be charged at the 1/8th the 20 hour rate of the batteries. My Spec sheet for my FLA Trojans limit to that. To not go below 50% after two days, that is around 480ah usable per day or a daily power requirement of 23 kwh.
I have 4 - 48v 520ah batteries. That's 2080ah. So would that allow me to charge at 240amps?
 
I bought some used commercial panels and the issue I encountered was the same that @Samsonite801 mentioned.. They had a higher VOC and I had to calculate the string voltage of various string sizes for my Outback Skybox to work. AFAIK, charge controllers are not able to exceed their max string voltage and that is the issue, not the total Watts.
 
I have 4 - 48v 520ah batteries. That's 2080ah. So would that allow me to charge at 240amps?
I think the max charge rate would be 240 amps.

Important to get the battery spec. My much smaller FLA Trojan Golf Cart Batteries are rated for a 1/8 the 20 hour battery rate. FLA Forklift batteries I have looked into are the same charge rate. Other lead acid batteries I have seen are 1/10th.

A good spec to get is the discharge rate. After going below 50% my lead acid batteries take a nose dive in how long they will last. Perhaps forklift batteries can be discharged more. They are designed to be used for two shifts and then charged a shift to be ready for the next two.

Also, the 20 hour rate is used for these calculations. Sometimes batteries are advertised at the 100 hour rate which makes it look like more power. Just be sure that’s what the 520 ah rate is.

I just finished my upgrade to lithium from lead acid batteries. I had it enough panels and SCCs up so that I could exceed the max charge rate of my FLA. I had been using so little power, I was done charging by 10 am where that wasn’t an issue, but if I did have a deeper discharge rate and needed a few more hours, I would need to be careful. I’m told you can exceed the max charge rate for a little, but I doubt that means by an hour or more.
 
I think my maximum charge rate is 120 amps because no matter how low the batteries are or how high I turn up the generator, it will not exceed 120 amps charging rate. But that's for 2 520ah batteries in parallel. So 4 in parallel should be 240 amps.

These batteries were not taken care of properly in the first few years of there life. When I recieved the trailers, I had to add nearly a gallon of water to each cell. I've already replaced one bad cell and have another that needs replacing. I'll replace that one as well, but I'm going to do some test on it to see if I can rejuvenate it. I didn't think to do that with the first one I replaced. I hope to get a few more years use out of these batteries.

I can't find any spec sheets for these batteries, but I'm still looking.
 
Hey Ralo,

So the dilemma with your panels is they have very high 85.6 Voc rating on them. Looking at the calculations (going with LV6548), you could only get 2 panels in series, and 2 serial strings in parallel to be 100% safe (possibly might be able to go up to 3 in parallel), but it would go over the LV6548 max amperage spec (18a vs your 19.29a if 3 strings were in parallel)...

Some charge controllers like the Sol-Ark 12k for example will never draw up past their max amp rating, but some users here on the forum believe that on MPP Solar you could get into trouble with over-paneling on amps, as they say the MPP Solar PV circuit may have been designed to possibly allow it to draw more than its 18a max rating?

Me personally, I don't have any experience with this. You could ping peggy@mppsolar.com and ask her if she can find out whether it is safe/fine to put panels equaling 19.29a on the PV inputs for the LV6548 (even though its max rating is 18a per PV input channel), I wouldn't want to speculate, when I could ask someone who should be able to find out for sure.

The point is, if you could get 2 in series, and 3 series strings in parallel on a PV input, then that could potentially be up to 6 panels on one PV input, so 24 of your panels could go across four PV inputs on the two LV6548's.

That still leaves you 6 short, so you would have to get some other charge controller if you wanted to run those.

If you just went safer (say chose not to ping MPP Solar to ask), just wired 2 series, and 2 strings paralleled, you'd be able to have 4 panels per PV input (12.86a), and you could only get 16 panels on the four PV inputs on the two LV6548's...

The next question. How much inverter power do you need? You could either go with 2 more LV6548s (four total) to get more PV inputs, or if you don't need that much inverter, you could add more standalone charge controllers.

Or you could shop around and see what other inverter options are out there which may support higher max PV input Voc (not sure your budget).

Sol-Ark 12k for example has a higher max PV input of up to 500v and 2x MPPT channels (Max DC voltage 500V@18A, 450V@20A) to give more versatility, but they cost a bunch more than MPP Solar.

But for example, with a Sol-Ark 12k, you might be able to go as high as 5 in series, and 3 paralleled strings (per PV input), so you might be able to get all 30 panels on one Sol-Ark (basing on rough estimation, will have to confirm the coldest temperature with you to get exact number).
 
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Because I was striking out with lesser charge controllers and since these are high voltage commercial panels, I called SMA and the guy I talked to recommended two Sunny Boy SB5.0-1SP-US-41. It only puts out 5000w but excepts 3 strings up to 600v each. So I could put the 12 south facing panels on one inverter and the other 12 north facing and 6 west facing panels on the other inverter. And the icing on the cake is the Sunny Boys would be controlled by the Sunny Island inverters I already have. And I can get two Sunny Boy inverters for about $2500. I plan to sell two of my four Sunny Island inverters and the trailers they came on to recoup these expenses. Also, the Sunny Boy Inverter supports their Shade Fix optimizers if I ever want them so that's a plus.

So looks like I have the inverter/charger issue covered. The SI's will continue to charge my batteries with power provided by the Sunny Boys. One big happy family!

1641850019720.png1641849893605.png
 
Definitely keep the SMA Sunny Islands, don't replace with some inferior off-brand.
Sunny Boy is the way to add much more. If you wanted, you could install 24kW of Sunny Boy, have 12kW of AC loads and another 12kW charging battery.
That is within vendor quoted parameters, although I could imagine issues if 12kW of AC load shut off suddenly (it take a couple seconds to throttle back Sunny Boy output.)

Sunny Island tracks amps from Midnight but can't tell them to reduce. It will control charge current from generator or Sunny Boy to keep total current at desired level (but not less than what Midnight delivers.)

I think it is 6s Sunpower 435W that will best work for 600V max PV string, but double-check Voc and temperature coefficient calculations.
Probably one PV string per MPPT input, but you may be able to "over panel" with 6s2p on each input, one 6s aimed SE and one 6s SW, for more kWh/day without exceeding max kW.

With Midnight Classic connected and Sunny Boy disconnected, then the reverse, then both connected, ensure Sunny Island correctly shows battery current. It needs to be told about the shunt and it needs to do a self-calibration of the shunt. (One guy had a situation of both communication to Classing and Shunt which resulted in Sunny Island having issues with battery state of charge and damaging relays in Sunny Island, which they replaced under warranty.)

Although keeping the Classic in the system will get battery recharged eventually in the event it has discharged to 80% DoD and Sunny Island turns off, recharging to 50% DoD will take longer without Sunny Boy contributing. It is also inconvenient to have to turn things back on.

So I still suggest adding a "load shed" relay which disconnects all AC loads, leaving just Sunny Boy (and maybe phone, alarm, etc.) connected.
Also, select some non-critical loads to be shed at a higher SoC. For instance, air conditioning could be enabled only when > 80% SoC. That way you get as much cooling as PV can provide, but all other loads probably stay on all the time.

Because you are off-grid and don't need UL-1741-SA, you can also look for old model Sunny Boy. If they are second hand you will need grid-guard code to put them in off-grid mode. I've been able to buy 10000TLUS-12 (don't get the 208V only model) and 5000US for about $0.10/W, so cheaper than the new -40 or -41 models. See SMA's list of compatible models for off-grid.
 
Definitely keep the SMA Sunny Islands, don't replace with some inferior off-brand.
Sunny Boy is the way to add much more. If you wanted, you could install 24kW of Sunny Boy, have 12kW of AC loads and another 12kW charging battery.
That is within vendor quoted parameters, although I could imagine issues if 12kW of AC load shut off suddenly (it take a couple seconds to throttle back Sunny Boy output.)

Sunny Island tracks amps from Midnight but can't tell them to reduce. It will control charge current from generator or Sunny Boy to keep total current at desired level (but not less than what Midnight delivers.)

I think it is 6s Sunpower 435W that will best work for 600V max PV string, but double-check Voc and temperature coefficient calculations.
Probably one PV string per MPPT input, but you may be able to "over panel" with 6s2p on each input, one 6s aimed SE and one 6s SW, for more kWh/day without exceeding max kW.

With Midnight Classic connected and Sunny Boy disconnected, then the reverse, then both connected, ensure Sunny Island correctly shows battery current. It needs to be told about the shunt and it needs to do a self-calibration of the shunt. (One guy had a situation of both communication to Classing and Shunt which resulted in Sunny Island having issues with battery state of charge and damaging relays in Sunny Island, which they replaced under warranty.)

Although keeping the Classic in the system will get battery recharged eventually in the event it has discharged to 80% DoD and Sunny Island turns off, recharging to 50% DoD will take longer without Sunny Boy contributing. It is also inconvenient to have to turn things back on.

So I still suggest adding a "load shed" relay which disconnects all AC loads, leaving just Sunny Boy (and maybe phone, alarm, etc.) connected.
Also, select some non-critical loads to be shed at a higher SoC. For instance, air conditioning could be enabled only when > 80% SoC. That way you get as much cooling as PV can provide, but all other loads probably stay on all the time.

Because you are off-grid and don't need UL-1741-SA, you can also look for old model Sunny Boy. If they are second hand you will need grid-guard code to put them in off-grid mode. I've been able to buy 10000TLUS-12 (don't get the 208V only model) and 5000US for about $0.10/W, so cheaper than the new -40 or -41 models. See SMA's list of compatible models for off-grid.
I will test the system without the load shed relay. I don't mind getting up to turn things back on. I have done so many times in the middle of the night.

Now I'm just trying to decided on a roof mounting system. I want to attach to the purlins of my metal roof, not just the tin. Everything is so expensive.
 
Definitely keep the SMA Sunny Islands, don't replace with some inferior off-brand.
Sunny Boy is the way to add much more. If you wanted, you could install 24kW of Sunny Boy, have 12kW of AC loads and another 12kW charging battery.
That is within vendor quoted parameters, although I could imagine issues if 12kW of AC load shut off suddenly (it take a couple seconds to throttle back Sunny Boy output.)

Sunny Island tracks amps from Midnight but can't tell them to reduce. It will control charge current from generator or Sunny Boy to keep total current at desired level (but not less than what Midnight delivers.)

I think it is 6s Sunpower 435W that will best work for 600V max PV string, but double-check Voc and temperature coefficient calculations.
Probably one PV string per MPPT input, but you may be able to "over panel" with 6s2p on each input, one 6s aimed SE and one 6s SW, for more kWh/day without exceeding max kW.

With Midnight Classic connected and Sunny Boy disconnected, then the reverse, then both connected, ensure Sunny Island correctly shows battery current. It needs to be told about the shunt and it needs to do a self-calibration of the shunt. (One guy had a situation of both communication to Classing and Shunt which resulted in Sunny Island having issues with battery state of charge and damaging relays in Sunny Island, which they replaced under warranty.)

Although keeping the Classic in the system will get battery recharged eventually in the event it has discharged to 80% DoD and Sunny Island turns off, recharging to 50% DoD will take longer without Sunny Boy contributing. It is also inconvenient to have to turn things back on.

So I still suggest adding a "load shed" relay which disconnects all AC loads, leaving just Sunny Boy (and maybe phone, alarm, etc.) connected.
Also, select some non-critical loads to be shed at a higher SoC. For instance, air conditioning could be enabled only when > 80% SoC. That way you get as much cooling as PV can provide, but all other loads probably stay on all the time.

Because you are off-grid and don't need UL-1741-SA, you can also look for old model Sunny Boy. If they are second hand you will need grid-guard code to put them in off-grid mode. I've been able to buy 10000TLUS-12 (don't get the 208V only model) and 5000US for about $0.10/W, so cheaper than the new -40 or -41 models. See SMA's list of compatible models for off-grid.
Hedges, looks like you are right about the load-shedding device. The SMA manual mentions it several times and I thought I read somewhere this it is actually required...but I can't find that now. Anyway, that's another device I'll be incorporating into this system.

Now I'm trying to get a clear understanding of how to connect everything. I've been reading the SI manual, and I was surprised to learn that the SB connects to AC1 which is also where the loads are connected. I guess that means AC1 is bi-directional meaning input and output. Then I realized that AC2 is also bi-directional because that's where the generator/grid connects, and I've had my generator get backfed once the batteries were full. The SI would disconnect the generator with the error GnRvPwr so AC2 went from recieving power to supplying power. So I guess this means there is a connection between AC1 and the loads circuit breaker panel? That's output. Then the SB also connects to AC1, that's input.

Forgive me for being confused but I would have thought that the input and output would be separate. I fully expected the SB's to connect to the same input as the generator/grid...since the SI will be charging the batteries from the SB just like it does from the generator. Is there a schematic anywhere that shows how all this stuff connects together?

I've taken the cover off my SI's and loads panel trying to understand where everything is going and why. I think I'll keep a Midnite CC in the mix for DC battery charging outside of the SI. The SI is currently aware of it, so I plan on that continuing once the SB's are incorporated. Just trying to get a clear understanding or all the connections. I'll need that before I'm comfortable connecting everything. All guidance appreciated.

Thanks!
 

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Not sure there is a great schematic, maybe various block diagrams.

Sunny Boy GT PV would backfeed through SI AC output to AC input, if SI thinks grid is connected and backfeed is enabled.
"Grid Charge" would tell it not to backfeed.
"Gen" would tell it not to backfeed.
If both grid and generator present, a digital input is used to tell SI which is connected.

With Midnight, if it charges battery to higher voltage than SI's target an "Grid Feed" is enabled, then SI backfeeds grid.

"Ground" is same net for both AC input and AC output.
"Neutral" is same net for both AC input and AC output.
In fact, for my setup, I only connected a single Ground wire and a single Neutral wire. The star connection occurs at protected loads panel rather than inside SI.
A SPST relay connects "Line" between AC input and AC output, when SI decides. (Really a 3PDT relay, but used as SPDT. All contacts in parallel, or maybe 2 in parallel to handle current plus 3rd to let SI confirm state of relay?)

You could operate without load-shed, but would be a pain to recover if no DC coupled charging source. With suitable shedding, should never stop working.

AC output (AC1?) goes to loads and sunny boys. You want sunny boys always connected and loads after the load-shed relay. So either fork the circuit to two panels (one switched by relay), or first goes to Sunny Boy panel, then relay, then loads panel.

Sunny boys don't go to same circuit as generator/grid. If they did, they would backfeed grid, or backfeed generator, or shut off if neither present. They go the the "island" or loads side, to remain running when SI forms the grid, and to respond to SI's frequency shift.

Older documents showed more. Neither of these distinguishes AC1 from AC2


This is even worse, shows "AC (line 1)" and "AC (line 2)" going to both house and sunny boys.


Maybe you can find other older diagrams somewhere. Otherwise, RTFM (it's all you've got), post sketches/photos, and ask questions.
 
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